Image relay optical system and virtual image display device including the same

ABSTRACT

An image relay optical system is provided with an optical coupling member before incidence of image light on a light guide member. Among a first light incident surface, a coupling member reflecting surface, and a first light emitting surface provided in the optical coupling member, the coupling member reflecting surface and the first light emitting surface are curved surfaces. Therefore, a large bright virtual image with reduced aberration can be displayed.

This is a Divisional Application of application Ser. No. 13/419,099filed Mar. 13, 2012 which claims priority to JP 2011-062542 filed Mar.22, 2011. The disclosure of the prior application is hereby incorporatedby reference herein in its entirety.

BACKGROUND

1. Technical Field

The present invention relates to an image relay optical system used fora head mounted display mounted on the head and used and a virtual imagedisplay device including the image relay optical system.

2. Related Art

In recent years, as a virtual image display device for enablingformation and observation of a virtual image such as a head mounteddisplay, various virtual image display devices of a type for guidingimage light from a display device to the pupils of an observer with alight guide plate are proposed. As the light guide plate for suchvirtual image display device, there is a light guide plate including alight guide pipe that can cause plural optical modes having differentlight guide angles to proceed (see JP-T-2008-535001).

In an optical system disclosed in JP-T-2008-535001, a liquid crystalpanel is illuminated with collimated light set to a different incidentangle for each of the optical modes on condition that images in theplural optical modes are positionally shifted from one another. Displaycontents are changed in the optical modes and displays in the opticalmodes are sequentially executed to join images in the optical modes andobtain an overall image. In this case, an image in the center and imageson the left and right included in the overall image have to be displayedwhile being changed with a time lag by one liquid crystal panel. As aresult, a virtual image display device is complicated and an observationimage is darkened.

There is also a virtual image display device for enabling observation ofa virtual image with a light guide member in which a concave reflectingsurface is provided accompanying a light incident surface and a convexreflecting surface is provided accompanying a light emitting surface. Inthe virtual image display device, it is unnecessary to join images witha time lag (see U.S. Pat. No. 7,477,453). An afocal system is formed bythe two inclining reflecting surfaces. Aberration such as distortion isnot reduced. Therefore, a projection optical system for collimate iscomplicated and image processing is necessary.

SUMMARY

An advantage of some aspects of the invention is to provide an imagerelay optical system that can simply display a large bright virtualimage with relatively small aberration and a virtual image displaydevice incorporating the image relay optical system.

An aspect of the invention is directed to an image relay optical systemincluding (a) an optical coupling member that is formed of a lighttransmissive material and on which image light is made incident and (b)a light guide member that is formed of a light transmissive material andguides the image light from the optical coupling member and emits theimage light to the outside. (c) The optical coupling member includes atleast a first light incident surface, a coupling member reflectingsurface, and a first light emitting surface in order of incidence of theimage light. (d) At least one of the first light incident surface, thecoupling member reflecting surface, and the first light emitting surfaceis a curved surface. (e) The light guide member includes at least asecond light incident surface, first and second total reflectingsurfaces opposed to and extending in parallel to each other, a lightguide member reflecting surface, and a second light emitting surface.(f) The light guide member reflecting surface is a curved surface. (g)The second light emitting surface is a flat surface. In the image relayoptical system, the optical coupling member is provided before theincidence of the image light on the light guide member. At least one ofthe first light incident surface, the coupling member reflectingsurface, and the first light emitting surface provided in the opticalcoupling member is the curved surface. Therefore, it is possible todisplay a large bright virtual image with reduced aberration.

A specific aspect of the invention is directed to the image relayoptical system, wherein the coupling member reflecting surface is atotal reflection mirror that reflects most of the image light and thelight guide member reflecting surface is a concave convergent surfacethat converts the image light, which is focused as an intermediate imagein the light guide member, into parallel beams. The total reflectionincludes reflecting nearly 100% of light by, for example, providing areflection film. In this case, a loss of light on the coupling memberreflecting surface is reduced. A substantially infinite virtual imagecan be formed by the conversion into the parallel beams on the lightguide member reflecting surface.

Another aspect of the invention is directed to the image relay opticalsystem, wherein in the optical coupling member, the first light incidentsurface is a surface functioning as a total reflecting surface, thecoupling member reflecting surface is a concave convergent surface, andthe first light emitting surface is a convex convergent surface. In thelight guide member, the second light incident surface is a convexconvergent surface. In this case, the convergent surfaces provided inthe optical coupling member and the light guide member enable correctionof distortion and the like. A bright virtual image with reducedaberration can be formed. A loss of light is reduced by the totalreflection on the first light incident surface.

Still another aspect of the invention is directed to the image relayoptical system, wherein in the optical coupling member, the first lightincident surface is a convex convergent surface, the coupling memberreflecting surface is a concave convergent surface, and the first lightemitting surface is a convex convergent surface. In the light guidemember, the second light incident surface is a convex convergentsurface. In this case, the convergent surfaces provided in the opticalcoupling member and the light guide member enable correction ofdistortion and the like. A bright virtual image with reduced aberrationcan be formed.

Yet another aspect of the invention is directed to the image relayoptical system, wherein in the optical coupling member, the first lightincident surface is a convex convergent surface, the coupling memberreflecting surface is a concave convergent surface, and the first lightemitting surface is a convex convergent surface. In the light guidemember, the second light incident surface is a surface functioning as afirst total reflecting surface. The light guide member includes a totalreflection opposed reflecting surface that includes a concave convergentsurface opposed to the second light incident surface and reflects theimage light from the second light incident surface to the first totalreflecting surface. The image relay optical system includes a convergentlens arranged between the first light emitting surface of the opticalcoupling member and the second light incident surface of the light guidemember. In this case, the convergent surfaces provided in the opticalcoupling member and the light guide member enable correction ofdistortion and the like. The convergent lens arranged between the firstlight emitting surface and the second light incident surface enablesadjustment of beams of the image light. Consequently, a bright virtualimage with reduced aberration can be formed.

Still yet another aspect of the invention is directed to the image relayoptical system, wherein in the optical coupling member, the first lightincident surface is a surface functioning as a total reflecting surface,the coupling member reflecting surface is a total reflection concaveconvergent surface, and the first light emitting surface is a convexconvergent surface. In the light guide member, the second light incidentsurface is a convex convergent surface. The image relay optical systemincludes a convergent lens arranged to be opposed to the first lightincident surface of the optical coupling member. In this case, theconvergent surfaces provided in the optical coupling member and thelight guide member enable correction of distortion and the like. A lossof light is reduced on the optical coupling member and the couplingmember reflecting surface. Further, the convergent lens arranged to beopposed to the first light incident surface of the optical couplingmember enables adjustment of beams of the image light. Consequently, abright virtual image with reduced aberration can be formed.

Further another aspect of the invention is directed to the image relayoptical system, wherein the light guide member reflecting surface of thelight guide member is a semi-transmissive mirror. The image relayoptical system includes a light transmitting member that includes acurved surface joined to the semi-transmissive mirror and makes itpossible to see an external image through the second light emittingsurface and the light guide member reflecting surface. In this case, thelight transmitting member joined to the back of the semi-transmissivemirror enables satisfactory see-through observation.

Still further another aspect of the invention is directed to the imagerelay optical system, wherein at least one of a refractive index anddispersion of the optical coupling member is different from a refractiveindex and dispersion of the light guide member. In this case, variouskinds of aberration including chromatic aberration of the image lightcan be corrected by adjusting the reflective index and the dispersionbetween the optical coupling member and the light guide member. Yetfurther aspect of the invention is directed to a virtual image displaydevice including the image relay optical system explained above and animage forming device that forms image light guided by the image relayoptical system. In this case, the virtual image display device cansimply display a large bright virtual image with relatively smallaberration by using the image relay optical system.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a plan view showing a one eye side of an image relay opticalsystem and a virtual image display device incorporating the image relayoptical system according to a first embodiment.

FIG. 2 is a plan view showing the entire virtual image display device.

FIG. 3 is a perspective view showing a light transmitting member.

FIG. 4 is a plan view showing a virtual image display device accordingto a second embodiment.

FIG. 5 is a plan view showing a virtual image display device accordingto a third embodiment.

FIG. 6 is a plan view showing a virtual image display device accordingto a fourth embodiment.

FIG. 7 is a plan view showing an image relay optical system according toa modification.

DESCRIPTION OF EXEMPLARY EMBODIMENTS First Embodiment

An image relay optical system for a virtual image display device and avirtual image display device incorporating the image relay opticalsystem according to a first embodiment of the invention are explainedbelow with reference to the accompanying drawings.

A. Structure of the Image Relay Optical System and the Virtual ImageDisplay Device

A virtual image display device 100 according to this embodiment shown inFIG. 1 is applied to a headmounted display and includes an image formingdevice 10 and an image relay optical system 20 as a set.

The virtual image display device 100 causes an observer to recognizeimage lights generated by a virtual image and causes the observer toobserve an external image in a see-through manner. FIG. 1 shows only thevirtual image display device 100 for the left eye. However, as theentire virtual image display device 100, the set of the image formingdevice 10 and the image relay optical system 20 is provided tocorrespond to each of the right eye and the left eye of the observer.Since the virtual image display device 100 for the right eye and thevirtual image display device 100 for the left eye are symmetrical, onlythe virtual image display device 100 for the left eye is explained.Detailed explanation of the virtual image display device 100 for theright eye is omitted. As shown in FIG. 1, the image forming device 10includes an illumination device 31 that emits two-dimensionalillumination light, a liquid crystal display device 32, which is atransmissive spatial light modulating device, and an emission angleadjusting member 33 arranged between the illumination device 31 and theliquid crystal display device 32. The liquid crystal display device 32spatially modulates the illumination light emitted from the illuminationdevice 31 and forms image lights that should be a display target such asa moving image. The emission angle adjusting member 33 changes anemission angle distribution of the illumination light according to aposition in a screen and adjusts the image lights emitted from anemitting surface 32 a of the liquid crystal display device 32 such thatthe image lights are efficiently made incident on an eye EY of theobserver. The image relay optical system 20 includes an optical couplingmember 21, a light guide member 22, and a light transmitting member 23.The optical coupling member 21 is a member that is formed of a lighttransmissive material and propagates image lights from the image formingdevice 10 while converging the image lights as appropriate and emits theimage lights to the light guide member 22. The light guide member 22 isa member that is formed of a light transmissive material and guides theimage lights from the optical coupling member 21 and finally emits theimage lights to the outside as image lights converted into parallelbeams. The light transmitting member 23 is formed of a lighttransmissive material having a refractive index same as the refractiveindex of the light guide member 22. The light transmitting member 23 isjoined to the interior side of the light guide member 22 and enables theobserver to see an external image through the light transmitting member23. As shown in FIG. 2, the light transmitting member 23 is arrangedbetween a pair of light guide members 22, 22 provided to correspond tothe left and right eyes EY, EY of the observer and is joined to the pairof light guide members 22, 22. Consequently, the pair of light guidemembers 22, 22 and the light transmitting member 23 are connected andintegrated as one member. In other words, the light transmitting member23 is a suspended member suspended from one light guide member 22 to theother light guide member 22.

As shown in FIG. 1, the optical coupling member 21 is a columnar lightguide member extending in a Y direction and includes a first lightincident surface 21 a, a coupling member reflecting surface 21 b, and afirst light emitting surface 21 c. When a route of the image lights isconsidered, the surfaces 21 a, 21 b, and 21 c are arrayed in order ofincidence of the image lights. A connecting surface CF1, which is asurface for connecting the first light incident surface 21 a and thecoupling member reflecting surface 21 b and is not optically used, ispresent between the first light incident surface 21 a and the couplingmember reflecting surface 21 b. A connecting surface CF2 is presentbetween the coupling member reflecting surface 21 b and the first lightemitting surface 21 c. The first light incident surface 21 a and thefirst light emitting surface 21 c are adjacent to and directly connectedto each other. Among these optically used surfaces, the first lightincident surface 21 a is a flat surface extending while being opposed tothe emitting surface 32 a of the liquid crystal display device 32 and isa surface for capturing the image lights emitted from the image formingdevice 10 into the optical coupling member 21. The first light incidentsurface 21 a includes an extended surface ES, which is a surface on anextended region outside a region on which the image lights are madeincident from the image forming device 10. The coupling memberreflecting surface 21 b is a concave convergent surface (specifically, aconcave spherical surface or aspherical surface). The coupling memberreflecting surface 21 b includes a reflection film ML, which is formedby aluminum evaporation or the like, to function as a total reflectionmirror that reflects most of the image lights captured from the firstlight incident surface 21 a. In other words, nearly 100% of the imagelights are reflected by the reflection film ML. The first light emittingsurface 21 c is a convex convergent surface (specifically, a convexspherical surface or aspherical surface). The first light emittingsurface 21 c emits the image lights to the light guide member 22 locatedon a downstream side in an optical path.

The light guide member 22 is a tabular light guide member extending in aYZ direction and includes a second light incident surface 22 a, firstand second total reflecting surfaces 22 b and 22 c, a light guide memberreflecting surface 22 d, and a second light emitting surface 22 e. Whenthe route of the image lights is considered, the surfaces 22 a, 22 b, 22c, 22 d, and 22 e are arrayed in order of incidence of the image lights.A connecting surface CF 3 is present between the second light incidentsurface 22 a and the second total reflecting surface 22 c. Adjacentsurfaces of the other surfaces are directly connected to each other.Among these optically used surfaces, the second light incident surface22 a is a convex convergent surface (specifically, a convex sphericalsurface or aspherical surface). The second light incident surface 22 ais arranged to be opposed to the first light emitting surface 21 c ofthe optical coupling member 21. The image lights emitted from theoptical coupling member 21 are made incident on the second lightincident surface 22 a. The first and second total reflecting surfaces 22b and 22 c are surfaces extending in a Z direction in an opposed andparallel state. The first and second total reflecting surfaces 22 b and22 c guide the image lights made incident from the second light incidentsurface 22 a from an entrance side to an interior side in the lightguide member 22 by totally reflecting the image lights. The light guidemember reflecting surface 22 d is a concave convergent surface(specifically, a concave spherical surface or aspherical surface). Thelight guide member reflecting surface 22 d bends the image lights whileconverting the image lights into parallel beams. The light guide memberreflecting surface 22 d is formed as a semi-transmissive mirroraccompanied by a half mirror layer 24, which is a reflection film havingtransmissivity (i.e., a semi-transmissive reflection film). The secondlight emitting surface 22 e is a surface present on the extension of thesecond total reflecting surface 22 c and extending along a flat surface,i.e., a YZ plane. The second light emitting surface 22 e emits the imagelights, which have passed through the light guide member reflectingsurface 22 d, to the eyes of the observer. In other words, the imagelights are emitted from the second light emitting surface 22 e to theoutside of the light guide member 22 and reach the eye EY of theobserver.

As explained above, both of the optical coupling member 21 and the lightguide member 22 include the concave and convex curved surfaces(specifically, the first light emitting surface 21 c, the second lightincident surface 22 a, etc.) to make it possible to change states ofconvergence and divergence of the image lights. The shapes of the curvedsurfaces defined by a curvature, a curvature center, an asphericalcoefficient, and the like are adjusted as appropriate to applyreflection and refraction action matching the arrangement of the curvedsurfaces to the image lights. This makes it possible to reduceoccurrence of aberration represented by distortion. In the opticalcoupling member 21 and the light guide member 22, at least one ofcharacteristics of a refractive index and dispersion are set differentfrom each other to vary the reflection and refraction action applied tothe image lights. This makes it possible to cope with occurrence ofchromatic aberration.

As shown in FIGS. 1 to 3, the light transmitting member 23 has arefractive index same as the refractive index of the main body of thelight guide member 22 and includes a first surface 23 a, a secondsurface 23 b, and a third surface 23 c. The first and second surfaces 23a and 23 b extend onto extended planes of the first and second totalreflecting surfaces 22 b and 22 c along the YZ plane. The third surface23 c is formed as a curved surface arranged along the light guide memberreflecting surface 22 d of the light guide member 22. In other words,the light transmitting member 23 is formed as a member including awedge-like member WP held between the second surface 23 b and the thirdsurface 23 c. The third surface 23 c is formed as a joined surfacejoined to the half mirror layer 24 of the light guide member 22. Likethe light guide member 22, the light transmitting member 23 indicateshigh light transmissivity in a visible range. Therefore, it is possibleto see an external image through the second light emitting surface 22 eand the light guide member reflecting surface 22 d of the light guidemember 22. For example, the observer can observe image light GL reducedto 20% and external light GL′ reduced to 80% superimposed one on top ofthe other by the adjustment of the reflectance of the half mirror layer24.

B. Optical Paths of Image Lights

Optical paths of image lights are explained below. Among components ofimage lights emitted from the image forming device 10 shown in FIG. 1,optical paths of image lights GL1, GL2, and GL3 emitted from the centerand both the end sides of the liquid crystal display device 32 aretraced and explained. Optical paths of components of the other imagelights are intermediate optical paths of the optical paths of the imagelights GL1, GL2, and GL3 and are the same as the optical paths of theimage lights GL1, GL2, and GL3. Therefore, explanation of the opticalpaths is omitted.

First, the image light GL1 emitted from the center on the emittingsurface 32 a of the liquid crystal display device 32 is emitted to theoptical coupling member 21 in a state in which the image light GL1diverges from one point on the emitting surface 32 a. The image lightGL1 is made incident on the first light incident surface 21 a, which isa flat surface. The image light GL1 passing through the first lightincident surface 21 a and propagating in the optical coupling member 21is reflected on the coupling member reflecting surface 21 b. When theimage light GL1 is reflected, since the coupling member reflectingsurface 21 b is a concave convergent surface, the image light GL2changes to a state in which the image light GL2 is converted intosubstantially parallel beams. A traveling direction of the image lightGL2 is bent. The image light GL2 travels to the first light incidentsurface 21 a again. An angle with respect to the first light incidentsurface 21 a and an incident position of the image light GL1 change fromthose during first incidence according to the reflection action on thecoupling member reflecting surface 21 b. In this case, the image lightGL1 is adapted to be made incident at an angle at which the image lightGL1 is totally reflected without requiring a reflection film or thelike, i.e., an angle equal to or larger than a critical angle on thefirst light incident surface 21 a including the extended surface ES. Inother words, the first light incident surface 21 a in this casefunctions as a total reflecting surface that totally reflects the imagelight GL1. According to the total reflection, the image light GL1travels to the first light emitting surface 21 c while hardly losing alight amount. The image light GL1 is subjected to converging action onthe first light emitting surface 21 c and emitted from the first lightemitting surface 21 c to the light guide member 22. Consequently, theimage light GL1 emitted from the optical coupling member 21 is madeincident on the second light incident surface 22 a of the light guidemember 22.

Subsequently, the image light GL1 captured into the light guide member22 from the second light incident surface 22 a is subjected to theconverging action on the second light incident surface 22 a.Specifically, both of the first light emitting surface 21 c and thesecond light incident surface 22 a are convex convergent surfaces and,according to the refraction action on the surfaces, the image light GL1changes from a state in which the image light GL1 is converted intosubstantially parallel beams to a state in which the image light GL1converges. The image light GL1 passed through the second light incidentsurface 22 a is first totally reflected on the first total reflectingsurface 22 b located on a +X side of the first and second totalreflecting surfaces 22 b and 22 c opposed to and extending in parallelto each other in the Z direction, i.e., parallel to the YZ plane.Thereafter, the image light GL1 is totally reflected on the second totalreflecting surface 22 c located on a −X side. While being totallyreflected on the total reflecting surfaces 22 b and 22 c in this way,the image light GL1 in the converged state is once focused and thenchanges to the diverged state again and travels to the light guidemember reflecting surface 22 d. The light guide member reflectingsurface 22 d is a concave convergent surface. Therefore, the opticalpath of the image light GL1 is bent according to the reflection actionon the light guide member reflecting surface 22 d. The image light GL1changes from the diverged state to the converted state into parallelbeams and travels to the second light emitting surface 22 e. The imagelight GL1 is emitted as parallel beams, which form a virtual image, tothe eye EY of the observer perpendicularly to a +Z direction from thecenter side of the second light emitting surface 22 e, i.e., in a −Xdirection.

The image light GL2 emitted from the end on a +Z side on the emittingsurface 32 a of the liquid crystal display device 32 and the image lightGL3 emitted from the end on a −Z side on the emitting surface 32 a ofthe liquid crystal display device 32 follow optical paths similar to theoptical path of the image light GL1. Specifically, the image lights GL2and GL3 are emitted to the optical coupling member 21 in a state inwhich the image lights GL2 and GL3 diverge from one point on theemitting surface 32 a, pass through the surfaces of the optical couplingmember 21 and the light guide member 22, and, after once being focusedin the light guide member 22, are emitted to the eye EY of the observeras virtual image lights. The image light GL2 is emitted at an acuteangle with respect to the +Z direction along the second light emittingsurface 22 e when the image light GL2 passes through the second lightemitting surface 22 e. The image light GL3 is emitted at an obtuse anglewith respect to the +Z direction along the second light emitting surface22 e when the image light GL3 passes through the second light emittingsurface 22 e. All components of the image lights GL2 and GL3 and theother image lights other than the image light GL1 are subjected to therefraction and reflection action at different degrees on the first lightincident surface 21 a, the first light emitting surface 21 c, the secondlight incident surface 22 a, and the like having the concave and convexcurved surface shapes.

In general, when image light is emitted from an oblique direction or areflection optical system is used, aberration such as distortionparticularly tends to occur. Therefore, in the optical system in thisembodiment, it is highly likely that aberration occurs. On the otherhand, in the image relay optical system 20, all the components of theimage lights are subjected to the refraction and reflection action atdifferent degrees on the first light emitting surface 21 c, the secondlight incident surface 22 a, and the like. Therefore, the image relayoptical system 20 enables correction of distortion that occurs in theimage relay optical system 20. In correcting the distortion, the imagerelay optical system 20 also enables correction of chromatic aberration.

All the beams of the image lights change to the diverged state and thentravel to the light guide member reflecting surface 22 d after oncebeing focused in the light guide member 22. Therefore, when the imagelights are emitted from the image relay optical system 20, the imagelights are converted into parallel beams by the light guide memberreflecting surface 22 d, which is the concave convergent surface. Inother words, the light guide member reflecting surface 22 d is a surfacefor converting image lights focused as an intermediate image intoparallel beams in the light guide member 22. The image lights convertedinto the parallel beams on the light guide member reflecting surface 22d are combined in the position of the eye EY of the observer andrecognized as a virtual image. As explained above, the image lights aremade incident on the light guide member reflecting surface 22 d in astate in which the image lights are already subjected to correction ofdistortion or the like further on an upstream side in the optical paththan the light guide member reflecting surface 22 d. Therefore, theimage lights passed through the light guide member reflecting surface 22d are in a satisfactory state in which the image lights are corrected.When aberration occurs because of the reflection on the light guidemember reflecting surface 22 d, the image lights can be corrected in theoptical system further on the upstream side on the optical path than thelight guide member reflecting surface 22 d taking into account even thisaberration in advance. As explained above, chromatic aberration of theimage lights can also be corrected by adjusting the refractive indexesand the dispersion of the optical coupling member 21 and the light guidemember 22. In this case, since the image relay optical system 20includes the curved surfaces, an angle of view ϕ of the image lightsindicated by the image light GL2 to the image light GL3 can be setrelatively large on the eye EY side. Further, the width of the parallelbeams converted from the image lights can be increased. As a result, aneye ring diameter PP, which is an effective pupil diameter, can beincreased.

In the total reflection on all of the first light incident surface 21 aand the first and second total reflecting surfaces 22 b and 22 c, theimage light GL2 among the components of the image lights has the largesttotal reflection angle. On the other hand, the image light GL3 has thesmallest total reflection angle. Therefore, if the image light GL3having strictest condition is adapted to propagate at an angle thatsatisfies the total reflection condition, all the image lights can betotally reflected without requiring a reflection film or the like.

As explained above, the light guide member reflecting surface 22 d isthe semi-transmissive half mirror surface and the light transmittingmember 23 is formed of the light transmissive material. Therefore, theobserver can recognize the external light GL′ together with the imagelights via the light transmitting member 23 and the light guide memberreflecting surface 22 d.

As explained above, in the image relay optical system 20 according tothis embodiment, the optical coupling member 21 is provided before theincidence of the image lights on the light guide member 22. The curvedsurface is present among the first light incident surface 21 a, thecoupling member reflecting surface 21 b, and the first light emittingsurface 21 c provided in the optical coupling member 21. Therefore, alarge bright virtual image with reduced aberration can be displayed. Inthis case, since the image relay optical system 20 includes the twosections: the optical coupling member 21 and the light guide member 22,it is possible to hold an air layer between the optical coupling member21 and the light guide member 22 to provide a refractive indexdifference and increase action by refraction.

Second Embodiment

A second embodiment obtained by modifying the first embodiment isexplained below with reference to FIG. 4. An image relay optical systemand a virtual image display device according to this embodiment havestructure same as the structure shown in FIG. 1 except the opticalcoupling member 21 and the light guide member 22. Therefore, explanationis omitted concerning components serving as functional components of theimage forming device 10 and the like. The light transmitting member isnot shown in the figure.

As shown in FIG. 4, in this embodiment, in the optical coupling member21 of the image relay optical system 20, the first light incidentsurface 21 a is a convex convergent surface (specifically, a convexspherical surface or aspherical surface), the coupling member reflectingsurface 21 b is a concave convergent surface (specifically, a concavespherical surface or aspherical surface), and the first light emittingsurface 21 c is a convex convergent surface (specifically, a convexspherical surface or aspherical surface). In the light guide member 22,the second light incident surface 22 a is a convex convergent surface(specifically, a convex spherical or aspherical surface). Image lightsare subjected to the reflection and refraction action as appropriate bythese surfaces.

In this case, the image lights GL1, GL2, and GL3 emitted from the imageforming device 10 are made incident on the optical coupling member 21from the first light incident surface 21 a and totally reflected on thecoupling member reflecting surface 21 b to be converted intosubstantially parallel beams. The image lights GL1, GL2, and GL3directly travel to the first light emitting surface 21 c withoutreturning to the first light incident surface 21 a side. The imagelights GL1, GL2, and GL3 are subjected to the converging action on thefirst light emitting surface 21 c and emitted from the first lightemitting surface 21 c.

Subsequently, the image lights GL1, GL2, and GL3 are made incident onthe second light incident surface 22 a of the light guide member 22,subjected to the converging action, and totally reflected on the firstand second total reflecting surfaces 22 b and 22 c opposed to andextending in parallel to each other in the Z direction. While beingtotally reflected, the image lights GL1, GL2, and GL3 are once focusedfrom the converged state, change to the diverged state again, and travelto the light guide member reflecting surface 22 d. The optical paths ofthe image lights GL1, GL2, and GL3 are bent by the reflection action onthe light guide member reflecting surface 22 d, which is a concaveconvergent surface (specifically, a concave spherical surface oraspherical surface). The image lights GL1, GL2, and GL3 change from thediverged state to the converted state into the parallel beams and travelto the second light emitting surface 22 e.

Consequently, when the image light GL1 passes through the second lightemitting surface 22 e, the image light GL1 is emitted to the eye EY ofthe observer perpendicularly to the +Z direction from the center side ofthe second light emitting surface 22 e, i.e., in the −X direction. Theimage light GL2 is emitted at an acute angle with respect to the +Zdirection along the second light emitting surface 22 e when the imagelight GL2 passes through the second light emitting surface 22 e. Theimage light GL3 is emitted at an obtuse angle with respect to the +Zdirection along the second light emitting surface 22 e when the imagelight GL3 passes through the second light emitting surface 22 e.

As explained above, in this embodiment, as in the first embodiment, alarge bright virtual image with reduced aberration can be displayed bythe curved surfaces of the optical coupling member 21 and the lightguide member 22.

Third Embodiment

A third embodiment obtained by modifying the first embodiment isexplained below with reference to FIG. 5. An image relay optical systemand a virtual image display device according to this embodiment havestructure same as the structure shown in FIG. 1 except the section fromthe optical coupling member 21 to the light guide member 22. Therefore,explanation is omitted concerning components serving as functionalcomponents of the image forming device 10 and the like. The lighttransmitting member is not shown in the figure.

As shown in FIG. 5, in this embodiment, in the optical coupling member21 of the image relay optical system 20, the first light incidentsurface 21 a is a convex convergent surface (specifically, a convexspherical surface or aspherical surface), the coupling member reflectingsurface 21 b is a concave convergent surface (specifically, a concavespherical surface or aspherical surface), and the first light emittingsurface 21 c is a convex convergent surface (specifically, a convexspherical surface or aspherical surface). In the light guide member 22,the second light incident surface 22 a is a plane functioning as a firsttotal reflecting surface. In other words, in the light guide member 22,the second light incident surface 22 a and the first total reflectingsurface 22 b are formed as an integral surface continuing to the sameplane. The light guide member 22 includes, as a surface opposed to thesecond light incident surface 22 a, an opposed reflecting surface 22 fbetween the second light incident surface 22 a and the second totalreflecting surface 22 c. The opposed reflecting surface 22 f is aconcave convergent surface (specifically, a concave spherical oraspherical surface) and is a total reflecting surface that includes thereflection film ML and reflects image lights from the second lightincident surface 22 a to the first total reflecting surface. Further, inthe image relay optical system 20, a convergent lens 25 (specifically aconvex spherical or aspherical lens) is arranged between the first lightemitting surface 21 c of the optical coupling member 21 and the secondlight incident surface 22 a of the light guide member 22. The imagelights are subjected to the reflection and refraction action asappropriate by these surfaces and the lens.

In this case, the image lights GL1, GL2, and GL3 emitted from the imageforming device 10 are made incident on the optical coupling member 21from the first light incident surface 21 a and totally reflected on thecoupling member reflecting surface 21 b. The image lights GL1, GL2, andGL3 travel to the first light emitting surface 21 c and are emitted fromthe first light emitting surface 21 c.

Subsequently, the image lights GL1, GL2, and GL3 are made incident onthe lens 25 and subjected to the refraction action to be converted intosubstantially parallel beams and made incident on the light guide member22.

Subsequently, the image lights GL1, GL2, and GL3 are made incident onthe second light incident surface 22 a of the light guide member 22 andreturned to the second light incident surface 22 a side by thereflection on the opposed reflecting surface 22 f while being subjectedto the converging action. When the image lights GL1, GL2, and GL3 arereturned, since an angle of the image lights GL1, GL2, and GL3 withrespect to the second light incident surface 22 a, i.e., the first totalreflecting surface 22 b changes, the image lights GL1, GL2, and GL3 aretotally reflected on the first total reflecting surface 22 b. The imagelights GL1, GL2, and GL3 are repeatedly totally reflected on the firstand second total reflecting surfaces 22 b and 22 c opposed to andextending in parallel to each other in the Z direction. While beingtotally reflected, the image lights GL1, GL2, and GL3 are once focusedfrom the converged state, change to the diverged state again, and travelto the light guide member reflecting surface 22 d. The optical paths ofthe image lights GL1, GL2, and GL3 are bent by the reflection action onthe light guide member reflecting surface 22 d, which is a concaveconvergent surface (specifically, a concave spherical surface oraspherical surface). The image lights GL1, GL2, and GL3 change from thediverged state to the converted state into the parallel beams and travelto the second light emitting surface 22 e.

Consequently, when the image light GL1 passes through the second lightemitting surface 22 e, the image light GL1 is emitted to the eye EY ofthe observer perpendicularly to the +Z direction from the center side ofthe second light emitting surface 22 e, i.e., in the −X direction. Theimage light GL2 is emitted at an acute angle with respect to the +Zdirection along the second light emitting surface 22 e when the imagelight GL2 passes through the second light emitting surface 22 e. Theimage light GL3 is emitted at an obtuse angle with respect to the +Zdirection along the second light emitting surface 22 e when the imagelight GL3 passes through the second light emitting surface 22 e.

As explained above, in this embodiment, as in the first and secondembodiments, a large bright virtual image with reduced aberration can bedisplayed by the curved surfaces of the optical coupling member 21 andthe light guide member 22.

Fourth Embodiment

A fourth embodiment obtained by modifying the first embodiment isexplained below with reference to FIG. 6. An image relay optical systemand a virtual image display device according to this embodiment havestructure same as the structure shown in FIG. 1 except the opticalcoupling member 21, the light guide member 22, and the like. Therefore,explanation is omitted concerning components serving as functionalcomponents of the image forming device 10 and the like. The lighttransmitting member is not shown in the figure.

As shown in FIG. 6, in this embodiment, in the optical coupling member21 of the image relay optical system 20, the first light incidentsurface 21 a is a plane functioning as a total reflecting surface, thecoupling member reflecting surface 21 b is a total reflection concaveconvergent surface (specifically, a concave spherical surface oraspherical surface), and the first light emitting surface 21 c is aconvex convergent surface (specifically, a convex spherical surface oraspherical surface). Specifically, in the optical coupling member 21,the first light incident surface 21 a includes an extended surface ES1,which is a surface on an extended region outside a region on which imagelights are made incident from the outside. The first light incidentsurface 21 a including the extended surface ES1 functions as a totalreflecting surface for the image lights as well. The coupling memberreflecting surface 21 b is a total reflecting surface and can reflectthe image lights reflected on the extended surface ES1. In the lightguide member 22, the second light incident surface 22 a is a convexconvergent surface (specifically, a convex spherical surface oraspherical surface). Further, in the image relay optical system 20, aconvergent lens 12 (specifically a convex spherical or aspherical lens)is arranged to be opposed to the first light incident surface 21 a ofthe optical coupling member 21 between the image forming device 10 andthe optical coupling member 21. The image lights are subjected to thereflection and refraction action as appropriate by these surfaces andthe lens.

In this case, the image lights GL1, GL2, and GL3 emitted from the imageforming device 10 are converted into substantially parallel beams by theconvergent lens 12, made incident on the optical coupling member 21 fromthe first light incident surface 21 a, and totally reflected on thecoupling member reflecting surface 21 b. The image lights GL1, GL2, andGL3 travel to the first light incident surface 21 a including theextended surface ES while being subjected to the converging action. Whenthe image lights GL1, GL2, and GL3 travel to the first light incidentsurface 21 a, since an angle of the image lights GL1, GL2, and GL3 withrespect to the first light incident surface 21 a changes, the imagelights GL1, GL2, and GL3 are totally reflected on the first lightincident surface 21 a. The image lights GL1, GL2, and GL3 totallyreflected on the first light incident surface 21 a are totally reflectedon the coupling member reflecting surface 21 b again and travel to thefirst light emitting surface 21 c while hardly losing a light amount.The image lights GL1, GL2, and GL3 are subjected to the convergingaction on the first light emitting surface 21 c and emitted from thefirst light emitting surface 21 c.

Subsequently, the image lights GL1, GL2, and GL3 are made incident onthe second light incident surface 22 a of the light guide member 22,subjected to the conversing action, and totally reflected on the firstand second total reflecting surfaces 22 b and 22 c opposed to andextending in parallel to each other in the Z direction. While beingtotally reflected, the image lights GL1, GL2, and GL3 are once focusedfrom the converged state, change to the diverged state again, and travelto the light guide member reflecting surface 22 d. The optical paths ofthe image lights GL1, GL2, and GL3 are bent by the reflection action onthe light guide member reflecting surface 22 d, which is a concaveconvergent surface (specifically, a concave spherical surface oraspherical surface). The image lights GL1, GL2, and GL3 change from thediverged state to the converted state into the parallel beams and travelto the second light emitting surface 22 e.

Consequently, when the image light GL1 passes through the second lightemitting surface 22 e, the image light GL1 is emitted to the eye EY ofthe observer perpendicularly to the +Z direction from the center side ofthe second light emitting surface 22 e, i.e., in the −X direction. Theimage light GL2 is emitted at an acute angle with respect to the +Zdirection along the second light emitting surface 22 e when the imagelight GL2 passes through the second light emitting surface 22 e. Theimage light GL3 is emitted at an obtuse angle with respect to the +Zdirection along the second light emitting surface 22 e when the imagelight GL3 passes through the second light emitting surface 22 e.

As explained above, in this embodiment, as in the first to thirdembodiments, a large bright virtual image with reduced aberration can bedisplayed by the curved surfaces of the optical coupling member 21 andthe light guide member 22.

Modification

Besides the embodiments explained above, for example, as shown in FIG.7, it is possible to reduce the thickness of the light guide member 22effectively utilizing components that follow an optical path such asimage light GG. Specifically, first, the image light GG passes throughthe light guide member reflecting surface 22 d of the light guide member22 and are totally reflected on the first surface 23 a of the lighttransmitting member 23. The image light GG totally reflected on thefirst surface 23 a passes through the light guide member reflectingsurface 22 d again and is totally reflected on the second light emittingsurface 22 e present on the extension of the second total reflectingsurface 22 c. The image light GG totally reflected on the second lightemitting surface 22 e travels to the light guide member reflectingsurface 22 d for the third time. This time, the image light GG isreflected on the light guide member reflecting surface 22 d and reachesthe eye EY of the observer. It is possible to realize a reduction inthickness of the light guide member 22 by increasing efficiency of useof image lights also making use of the image light GG that follows theoptical path explained above.

Others

The invention is explained according to the embodiments. However, theinvention is not limited to the embodiments and can be carried out invarious forms without departing from the spirit of the invention. Forexample, modifications explained below are also possible.

In the above explanation, the transmissive liquid crystal display deviceis used. However, the liquid crystal display device according to theembodiments is not limited to the transmissive liquid crystal displaydevice. Various liquid crystal display devices can be used. For example,a configuration including a reflective liquid crystal panel is alsopossible. A digital micro-mirror device or the like can also be usedinstead of the liquid crystal display device 32. A configurationincluding a self-emitting device represented by an LED array or an OLED(organic EL) is also possible. Further, a configuration including alaser scanner in which a laser beam source, a polygon mirror, and otherscanners are combined is also possible.

In the above explanation, the virtual image display device 100 includesthe set of the image forming device 10 and the image relay opticalsystem 20 to correspond to each of the right and left eyes. However, aconfiguration in which the image forming device 10 and the image relayoptical system 20 are provided for one of the right and left eyes toview an image with one eye may be adopted.

In the above explanation, the see-through virtual image display deviceis explained. However, when it is unnecessary to cause the observer toobserve an external image, it is possible to set the light reflectanceof the light guide member reflecting surface 22 d to about 100%.

In the above explanation, the virtual image display device 100 accordingto the embodiments is specifically explained assuming that the virtualimage display device 100 is the head mounted display. However, thevirtual image display device 100 according to the embodiments can bemodified to a head-up display.

In the above explanation, on the first and second total reflectingsurfaces 22 b and 22 c, the image lights can be totally reflected andguided by an interface with the air without applying a mirror, a halfmirror, or the like to the surfaces. However, the total reflection inthe invention includes reflection performed by forming a mirror coat ora half mirror film on all or a part of the first and second totalreflecting surfaces 22 b and 22 c. For example, on condition that anincident angle of image lights satisfies a total reflection condition, amirror coat or the like is applied to all or a part of the totalreflecting surfaces 22 b and 22 c and substantially all the image lightsare reflected. The total reflection includes the reflection in thiscase. If image lights having sufficient brightness are obtained, all ora part of the total reflecting surfaces 22 b and 22 c may be coated witha mirror slightly having transmissivity.

The entire disclosure of Japanese Patent Application No. 2011-062542,filed Mar. 22, 2011 is expressly incorporated by reference herein.

What is claimed is:
 1. An image relay optical system comprising: anoptical coupling member that is formed of a light transmissive materialand on which image light is made incident; and a light guide member thatis formed of a light transmissive material and guides the image lightfrom the optical coupling member and emits the image light to an outsideof the light guide member, wherein the optical coupling member includes,in order of incidence of the image light, at least (i) a first lightincident surface through which the image light enters the opticalcoupling member, (ii) a coupling member reflecting surface, which is asingle continuous reflecting surface, and (iii) a first light emittingsurface, and, the optical coupling member is configured so that imagelight entering the first light incident surface is transmitted towardthe single coupling member reflecting surface and is reflected off onlythe single coupling member reflecting surface, which reflects the imagelight toward the first light emitting surface where it is then emittedto the light guide member, the image light being reflected onlyinternally in the optical coupling member, the first light incidentsurface is a convex convergent surface, the single coupling memberreflecting surface is a concave convergent surface, and the first lightemitting surface is a convex convergent surface, the light guide memberincludes at least a second light incident surface, first and secondtotal reflecting surfaces opposed to and extending in parallel to eachother, a light guide member reflecting surface, and a second lightemitting surface, and the second light emitting surface is a flatsurface.
 2. The image relay optical system according to claim 1, whereinthe single coupling member reflecting surface is a total reflectionmirror that reflects most of the image light, and the light guide memberreflecting surface is a concave convergent surface that converts theimage light in the light guide member into parallel beams.
 3. The imagerelay optical system according to claim 2, wherein in the opticalcoupling member, the first light incident surface is a surfacefunctioning as a total reflecting surface, and in the light guidemember, the second light incident surface is a convex convergentsurface.
 4. A virtual image display device comprising: the image relayoptical system according to claim 3; and an image forming device thatforms the image light guided by the image relay optical system.
 5. Theimage relay optical system according to claim 2, wherein in the lightguide member, the second light incident surface is a convex convergentsurface.
 6. A virtual image display device comprising: the image relayoptical system according to claim 5; and an image forming device thatforms the image light guided by the image relay optical system.
 7. Theimage relay optical system according to claim 2, wherein in the lightguide member, the second light incident surface is a surface functioningas a first total reflecting surface, the light guide member including atotal reflection opposed reflecting surface that includes a concaveconvergent surface opposed to the second light incident surface andreflects the image light from the second light incident surface to thefirst total reflecting surface, and the image relay optical systemincludes a convergent lens arranged between the first light emittingsurface of the optical coupling member and the second light incidentsurface of the light guide member.
 8. A virtual image display devicecomprising: the image relay optical system according to claim 7; and animage forming device that forms the image light guided by the imagerelay optical system.
 9. The image relay optical system according toclaim 2, wherein in the optical coupling member, the first lightincident surface is a surface functioning as a total reflecting surface,the single coupling member reflecting surface is a total reflectionconcave convergent surface, in the light guide member, the second lightincident surface is a convex convergent surface, and the image relayoptical system includes a convergent lens arranged to be opposed to thefirst light incident surface of the optical coupling member.
 10. Avirtual image display device comprising: the image relay optical systemaccording to claim 9; and an image forming device that forms the imagelight guided by the image relay optical system.
 11. A virtual imagedisplay device comprising: the image relay optical system according toclaim 2; and an image forming device that forms the image light guidedby the image relay optical system.
 12. The image relay optical systemaccording to claim 1, wherein the light guide member reflecting surfaceof the light guide member is a semi-transmissive mirror, and the imagerelay optical system includes a light transmitting member that includesa curved surface joined to the semi-transmissive mirror and makes itpossible to see an external image through the second light emittingsurface and the light guide member reflecting surface.
 13. A virtualimage display device comprising: the image relay optical systemaccording to claim 12; and an image forming device that forms the imagelight guided by the image relay optical system.
 14. The image relayoptical system according to claim 1, wherein at least one of arefractive index and dispersion of the optical coupling member isdifferent from a refractive index and dispersion of the light guidemember.
 15. A virtual image display device comprising: the image relayoptical system according to claim 14; and an image forming device thatforms the image light guided by the image relay optical system.
 16. Avirtual image display device comprising: the image relay optical systemaccording to claim 1; and an image forming device that forms the imagelight guided by the image relay optical system.
 17. The image relayoptical system according to claim 1, wherein the light guide memberreflecting surface is a curved surface.
 18. The image relay opticalsystem according to claim 1, wherein the image relay optical system isconfigured so that image light incident on the light guide memberreflecting surface has already been subjected to correction ofdistortion or the like further upstream in the optical path.
 19. Theimage relay optical system according to claim 1, wherein the singlecoupling member reflecting surface is positioned on an opposite side ofthe optical coupling member from the first light incident surface.